Abstract
Natural gas is often coproduced with CO2 which need to be removed in order to increase the calorific value of the gas. High pressure membrane separation is one of the widely used technologies for this removal. However, one major challenge of high pressure operation is penetrant-induced plasticization phenomenon which is caused by increasing the feed pressure. High pressure gas permeation studies were performed to evaluate the plasticization response of a modified polysulfone membrane. This is necessary in order to establish the highest possible feed pressure which can be attained during CO2 removal without plasticization. Gas transport properties of the membrane were evaluated using permeation tests at pressure up to 57 bar. The dynamic evaluation of the response was done above and below the plasticization pressure using time-dependent permeation experiments over a period ranging from 5 hours to 1080 hours (45 days) at various pressures between 6 and 57 bar. The time-dependent permeability tests revealed a continuous decrease in permeability with time at pressure below the plasticization pressure but a continuous increase in permeability at pressure higher than the plasticization pressure. Generally, the overall results revealed that there is a certain pressure at which the two competing phenomena of physical aging and plasticization counter balance each other. This pressure was suspected to be at the plasticization pressure. It can be concluded that the economic advantage of high pressure operation is particularly true only if the membrane is maintained at an equilibrium pressure which coincides with the plasticization pressure.
